When an etching target layer is plasma-etched, a resist mask such as a photoresist or the like is used. Especially, a recent trend toward fine processing demands the use of an ArF photoresist or an F2 photoresist which is suitable for forming an opening pattern of a size no greater than about 0.13 μm, i.e., a photoresist exposed to a laser beam of which an emission source is ArF gas or F2 gas.
However, an ArF photoresist layer and an F2 photoresist layer have a low plasma resistance, so that their surfaces become rough during etching. The surface roughening of the photoresist layer causes deformation of the shape of the opening as the etching progresses. As a result, it is difficult to form an etching hole or an etching groove having a desired shape.
As for a method for improving plasma resistance of a photoresist layer, there are known a method for irradiating UV rays, electron rays or ion beams onto a surface of the photoresist layer (see, e.g., Japanese Patent Application Publication Nos. S60-110124, H2-252233 and S57-157523(corresponding to European Patent No. 0061350)), a method for hardening a photoresist by heating (Japanese Patent Application Publication No. H4-23425), and a method for coating a thin hardened layer on a surface of a photoresist layer by applying heat or beam energy to an organic Si compound (Japanese Patent Application Publication No. H2-40914).
However, in the above-described methods for improving plasma resistance of a photoresist layer, it is required to perform a plasma resistance improvement process in a chamber different from an etching chamber for a subsequent etching process. The transfer of a target object from the chamber for performing the plasma resistance improvement process to the etching chamber leads to a decrease in a yield in the transfer process or a decrease in a throughput due to the transfer time. Further, when the chamber for performing the plasma resistance improvement process and the etching chamber are independently provided, an additional space is required and cost is increased.
Meanwhile, if an etching target layer is directly covered by a photoresist layer, a dimensional accuracy of an opening pattern decreases when the opening pattern is formed by exposing and developing the photoresist layer. To that end, an antireflection layer is inserted between the etching target layer and the photoresist mask layer. In Japanese Patent Application Publication No. H10-261627, the antireflection layer is etched by a plasma of a gas containing a compound of C and F, e.g., a gaseous mixture of C4F8 and O2, a gaseous mixture of HBr, CF4 and He, or a gaseous mixture of CH2F2, CF4 and He. As for an etching gas for etching the antireflection layer, there is also known, e.g., a gaseous mixture of CF4 and O2 (Japanese Patent Application Publication No. H7-307328).
However, when the antireflection layer is etched by the plasma of the gaseous mixture of C4F8 and O2 or that of CF4 and O2, the surface of the photoresist layer becomes rough, or elongated strips are formed on the photoresist layer. Or, the photoresist layer may not serve as a mask layer due to excessive etching.
Therefore, in PCT Publication No. WO2004/003988 and its corresponding U.S. Patent Application Publication No. 2005-0103748, there has been proposed a method for etching an antireflection layer while improving plasma resistance of a photoresist layer (see, especially, the third embodiment thereof).
In WO2004/003988, the antireflection layer is etched by a plasma of a processing gas containing H2 gas, or a processing gas containing H2 gas and Ar gas, supplied into the etching chamber that has been exhausted. As a result, the plasma resistance of the photoresist layer is improved.
Compared to a method in which a process for improving plasma resistance of a photoresist layer is not performed, the method described in WO2004/003988 in which the plasma resistance of the photoresist layer is improved can suppress reduction in a height of the photoresist layer during the etching of the antireflection film.
However, the problem in which the height of the photoresist layer decreases remains unsolved. In some cases, the height of the photoresist layer becomes insufficient for etching.